Re: [PATCH] PCI: qcom: Ensure that PERST is asserted for at least 100 ms

From: Marc Gonzalez
Date: Fri May 24 2019 - 08:46:03 EST


On 23/05/2019 21:44, Niklas Cassel wrote:

> Currently, there is only a 1 ms sleep after asserting PERST.
>
> Reading the datasheets for different endpoints, some require PERST to be
> asserted for 10 ms in order for the endpoint to perform a reset, others
> require it to be asserted for 50 ms.
>
> Several SoCs using this driver uses PCIe Mini Card, where we don't know
> what endpoint will be plugged in.
>
> The PCI Express Card Electromechanical Specification specifies:
> "On power up, the deassertion of PERST# is delayed 100 ms (TPVPERL) from
> the power rails achieving specified operating limits."
>
> Add a sleep of 100 ms before deasserting PERST, in order to ensure that
> we are compliant with the spec.
>
> Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxxxx>
> ---
> drivers/pci/controller/dwc/pcie-qcom.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 0ed235d560e3..cae24376237c 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1110,6 +1110,8 @@ static int qcom_pcie_host_init(struct pcie_port *pp)
> if (IS_ENABLED(CONFIG_PCI_MSI))
> dw_pcie_msi_init(pp);
>
> + /* Ensure that PERST has been asserted for at least 100 ms */
> + msleep(100);
> qcom_ep_reset_deassert(pcie);
>
> ret = qcom_pcie_establish_link(pcie);

Currently, qcom_ep_reset_assert() and qcom_ep_reset_deassert() both include
a call to usleep_range() of 1.0 to 1.5 ms

Can we git rid of both if we sleep 100 ms before qcom_ep_reset_deassert?

Should the msleep() call be included in one of the two wrappers?

Regards.